The invention relates to a ceramic glass material, capacitors made using the material, and the method of making same. More particularly, the ceramic glass material provides a high dielectric constant with low dissipation factor and high insulation resistance when fired in a non oxidizing atmosphere to produce capacitors with non precious metal electrodes.
Ceramic glass capacitors have been produced by firing in air at low temperatures as disclosed in Pat. No. 3,619,220. Such capacitors however have required noble metal conductors which are resistant to oxidation. Use of non precious metal conductors such as copper has required firing in a low oxygen atmosphere and a special borosilicate glass formulation which is resistant to reduction and has a softening point below the melting point of the metal as described in Pat. No. 4,101,952. This patent also states that no known high dielectric constant glass ceramic materials are believed to be capable of sintering in a low partial oxygen atmosphere without experiencing greatly degraded electrical properties, and that oxides of lead, cadmium and bismuth have a major defect of being readily reduced and renders the material conductive when heated in a low partial atmosphere. Pat. No. 4,308,570 also teaches that in order to be reduction resistant when fired at a temperature of about 1050.degree. C. in an environment of about 10.sup.-11 atmospheres of oxygen, the oxides of lead, bismuth and cadmium must be excluded from the glass of a glass ceramic capacitor. The prior art, thus, teaches that the leaded glasses which have been found to be desirable for use in ceramic glass capacitors as disclosed in Pat. No. 3,619,220 are unsuitable for firing in a non oxidizing atmosphere necessary for co-firing with non precious or base metal electrodes. The use of leaded glass compositions, however, are desirable for producing the ceramic glass capacitors since they are highly compatible with the ceramic materials, bond tightly to substrates such as alumina and provide expansion coefficients which minimize separation and deterioration of the capacitors. This is especially important when capacitors are produced by a build up of a plurality of layers of dielectric and conductive materials. It is therefore desirable to provide a ceramic glass composition using leaded glass which can be fired in an non oxidizing atmosphere without deterioration to form a dielectric material with a low dissipation factor, and high insulation resistance and dielectric constant, and which can be co-fired with base metal conductors such as copper.